Conductive flow field plates comprise the outer layers of a fuel cell and serve a number of functions; they provide structural integrity to the fuel cell; protect the fuel cell from corrosive degradation over the operating life of the fuel cell; and, most importantly conduct electrons and heat from the interior of the fuel cell to the exterior. Conductivity at the interface between the flow field plate and the outermost interior layer, i.e., gas diffusion layer, is critical for minimizing fuel cell resistance.
Because of the unique set of performance requirements of conductive flow field plates and the aggressive conditions inside the fuel cell, the material options for constructing conductive flow field plates are limited. In general, graphite has been used for conductive flow field plates because of its high electrical conductivity and resistance to corrosion.
Carbon/graphite fillers over plastic polymers have been identified as a promising alternative to graphite in manufacturing conductive flow field plates. Processes for preparing such plates are disclosed in U.S. Pat. No. 4,124,747 A1 to Murer and Amadei, U.S. Pat. No. 4,169,816 A1 to Tsien and U.S. Pat. No. 4,686,072 A1 to Fukuda, which are hereby incorporated by reference.
While these carbon/graphite filler plates provide increased durability and flexibility to the fuel cell, the composition of carbon/graphite filler plates provides less than superior conductivity and resistivity (both bulk resistivity and through plane resistivity) properties. Attempts have been made to reduce the resistivity of a molded plate by machining the surface of the molded plate to eliminate the polymer rich skin layer from the surface of the plate. Such machining processes however are time consuming and expensive.
There therefore remains a need for a convenient post-molding process that improves the resistivity of conductive flow field plates.